When an ore block is broken using a Smashing enchanted pickaxe or similar tool, the ore is instantly crushed into two piles of dust (three if the ore is from the Nether or the End). This only works with ore blocks that drop themselves when broken. For example, iron ore drops two piles of pulverized iron and copper ore drops two piles of pulverized copper.
When a tool is enchanted with both Smashing and Smelting, the effect of Smashing is applied before that of Smelting when breaking a block, causing metal ores to drop multiple ingots when broken.
Smashing and Silk Touch cannot be applied on a tool at the same time.